Chemical processes often require multiple unit operations to produce a particular product stream. A particular unit operation may be a liquid-liquid contacting operation whereby two liquids are brought into intimate contact to effectuate mass transfer between the liquids, a reaction between components in the liquids, or both. Liquid-liquid contacting may be beneficial in some types of chemical reactions where one reactant is miscible in a first liquid but immiscible in a second liquid. An example of such a reaction may be where a first reactant is present in a polar solvent such as water and a second reactant is present in a non-polar solvent such as a hydrocarbon and the water and hydrocarbon are immiscible. Liquid-liquid contacting may have other applications such as liquid-liquid extraction whereby a species present in a first liquid is extracted into a second liquid by mass transfer across the liquid-liquid interface.
A particular challenge of liquid-liquid contacting may be ensuring adequate contact area between the two liquids such that the mass transfer or reactions may occur in an appreciable amount and in an economically viable manner. In general, liquid-liquid contacting operations may be performed with immiscible liquids, such as, for example, an aqueous liquid and an organic liquid. Using two immiscible liquids may allow the liquids to be readily separated after the liquid-liquid contacting is completed. However, when a liquid-liquid contacting operation is performed with immiscible liquids, phase separation may occur before adequate contact between the liquids is achieved.
Several liquid-liquid contacting vessels and techniques have been developed to enhance the contact area between liquids in a liquid-liquid contacting process, including, but not limited to, fiber-bundle type liquid-liquid contactors. A fiber-bundle type liquid-liquid contactor may generally comprise one or more fiber bundles suspended within a shell and two or more inlets where the two liquids may be introduced into the shell. The fiber bundle may promote contact between the two liquids by allowing a first liquid to flow along individual fibers of the fiber bundles and a second liquid to flow between the individual fibers thereby increasing the effective contact area between the liquids. The two liquids may flow from an inlet section of the shell to an outlet section of the shell while maintaining intimate contact such that a reaction, mass transfer, or both may be maintained between the two liquids.
There may exist challenges with designing and operating fiber-bundle type liquid-liquid contactors due to “entrance effects” where the two liquids first come into contact. The degree to which the two liquids are mixed or in contact before they reach the fiber bundle may determine the effectiveness of liquid-liquid contact operation, the length of fiber required, pressure drop, material cost, and other factors apparent to those of ordinary skill in the art. Additionally, as the two liquids flow through the fiber bundle, when oriented vertically, phase separation may begin to occur such that the relatively heavier, or denser, liquid may begin to migrate to the center of the fiber-bundle while the relatively lighter, or less dense, liquid may begin to migrate to the outside of the fiber-bundle. Early phase separation may be a consequence of inadequate distribution of the two liquids before entering the fiber-bundle.